With recent higher performance of various industrial machinery and equipment, high temperatures, high pressure and high speeds are now conditions of sealing members use in the sliding parts of machinery. Thus, higher durability (heat resistance, pressure resistance and service longevity) is an important requirement for the sealing members. To attain the sealing performance of sealing members for a long time, it is necessary to improve the wear resistance. Fluids to be sealed include, for example, liquids such as engine oil, gear oil, transmission oil, long-life coolant, water, etc., and gases such as flon, carbon dioxide, nitrogen, hydrogen, natural gas, etc.
To improve the wear resistance, it has been proposed to mix the hydrogenated nitrile rubber with various fillers such as carbon black, silica, carbon fibers, etc., but no satisfactory and effective improvement of the wear resistance has been attained yet in many cases, though depending on use conditions of sealing members.
JP-A-2002-80639 proposes a hydrogenated nitrile rubber composition for use as a suitable molding material for sliding or high pressure sealing members with improved heat resistance, pressure deformation resistance, wear resistance, thermal conductivity, etc. The proposed hydrogenated nitrile rubber composition comprises 100 parts by weight of hydrogenated nitrile rubber having a bound AN content of not more than 38%, a hydrogenation degree of not less than 90% and an iodine number (median value) of not more than 28, and at least about 120 parts by weight of sum total of carbon black and other fillers, where the fillers comprises, for example, about 30 to about 100 parts by weight of carbon black, 10 to 60 parts by weight of graphite and about 5 to about 60 parts by weight of carbon fibers.
Indeed, high density filling of carbon fibers is effective for the improvement of wear resistance, but such problems as more frequent occurrences of bagging at the time of kneading with the hydrogenated nitrile rubber and other additives, poor flow in mold at the molding, etc. arise and actually molding cannot be carried out in many cases.